This invention relates to an ink jet printing process using an ink jet ink composition for improving the ozone and light stability of an ink jet image.
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods that may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant that is molecularly dispersed or solvated by a carrier medium. The carrier medium can be a liquid or a solid at room temperature. A commonly used carrier medium is water or a mixture of water and organic co-solvents. Molecules of the carrier medium surround each individual dye molecule. In dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor light-fastness. When water is used as the carrier medium, such inks also generally suffer from poor water-fastness.
A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. Many such compounds are known and are commercially used. Color Index International (publication by the Society of Dyers and Colorists, 1997) lists various classes of pigments. It is common practice to produce pigment compositions in the form of finely divided dispersions, which may be generated by well-known methods such as ball milling. In order to obtain the optimum dispersion properties it is common to have present at least one dispersant, and the choice of dispersant is important for achieving acceptable pigment dispersion properties. The purpose of the dispersant is to stabilize the particles and to prevent growth by aggregation and flocculation. However, merely adsorbing a dispersant to the pigment surface may lead to competition for such dispersant from solvents and humectants used in the ink formulation and may lead to desorption. In general, such systems may also suffer from a dependence on the concentration of the pigment, the type of humectants used, and the temperature and pH of the formulation containing the pigment. Therefore, it is often difficult to identify an acceptable dispersant which provides the needed ink stability and is compatible with other components in the ink formulation.
Images obtained from pigment-based inks generally have better light-fastness and ozone-fastness than that of the images obtained from dye-based inks. It is especially true when these are used with a recording element containing a porous image-receiving layer. However, pigment based inks have not received a wide degree of acceptance in ink jet ink systems, because of problems associated with the preparation, performance and reliability of the composition, such as dispersibility, print properties, dispersion stability, latency, smear, and gloss.
When a pigment-based ink is formulated, a dispersant is normally used along with a milling or physical grinding step. Alternatively, after milling, the pigment surface may be chemically modified to render the particles dispersible in an aqueous formulation. However, there is a problem with these techniques in that they take time and are expensive. It would be desirable to find alternative colorants having the image permanence of pigments but which do not require milling.
U.S. Pat. No. 5,922,118, EPA 0904327, and WO9747699 disclose surface-modified pigments, wherein such surface modification comprises ionic or ionizable groups for improvement of pigment dispersibility. However, these pigments still require a milling step.
It is an object of the invention to provide an ink jet printing process using an ink jet ink composition that employs self-dispersed particles that do not require milling or grinding and do not require the use of a dispersant.
This and other objects are achieved in accordance with the present invention that comprises an ink jet printing method comprising the steps of:
A) providing an ink jet printer that is responsive to digital data signals;
B) loading the printer with ink jet recording elements comprising a support having thereon an image-receiving layer;
C) loading the printer with an ink jet ink composition comprising water, humectant and a metallized, phthalocyanine colorant, the metallized, phthalocyanine colorant comprising the formula:
MPc(SO3X)a(SO2NRRxe2x80x2)b
xe2x80x83wherein: M represents a metal;
Pc represents a phthalocyanine nucleus;
each X independently represents hydrogen, alkali metal or an organic cation, such as Na, Li, or ammonium;
a is from 0 to 3;
b is from 1 to 4;
each R independently represents a substituted or unsubstituted alkyl group having from 1 to about 15 carbon atoms, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group;
each Rxe2x80x2 independently represents R or hydrogen; with the proviso that a+b is an average of from 2 to 4; and with the further proviso that at least about 50 wt. % of said metallized, phthalocyanine colorant is present in said composition as particles; and
D) printing on the image-receiving layer using the ink jet ink in response to the digital data signals.
It was found that the ozone and light stability of an ink jet image was improved when printing using the composition described herein.
In a preferred embodiment of the invention, R in the above formula represents a substituted or unsubstituted alkyl group having from 1 to about 15 carbon atoms containing a hydroxy group, a substituted or unsubstituted aryl group containing a hydroxy group or a substituted or unsubstituted heterocyclic group containing a hydroxy group. In another preferred embodiment, M in the above formula represents copper, nickel, aluminum, zinc, iron or cobalt. In another preferred embodiment, R in the above formula represents CH2CH2OH. In another preferred embodiment, M represents Cu or Ni and R is CH2CH2OH. In another preferred embodiment, at least about 70 wt. %, more preferably 80 wt. % of the metallized, phthalocyanine colorant is present in said composition as particles. In another preferred embodiment, the particles are less than about 0.3 xcexcm, more preferably less than about 0.1 xcexcm in size.
In another preferred embodiment of the invention, the metallized, phthalocyanine colorants that may be used include the following: 
Electrophilic substitution or construction of the phthalocyanine nucleus leads to a mixture of products. In each aromatic ring, as shown in the generalized structure below, substitution may occur at one of the 4 or 4a positions, which are equivalent, or at one of the 3 or 3a positions, which are equivalent.

The descriptors in Table 1a, xe2x80x98Substitutionxe2x80x99 column have the following meanings: 4, 4xe2x80x2, 4xe2x80x3, 4xe2x80x2xe2x80x3: substitution occurred to give one substituent in each aromatic ring at a 4 or 4a position; random:where substitution occurred, the substituent is present in one of the 3, 4, 4a or 3a positions in each aromatic ring.
Colorant A Composition is predominantly a mixture of Colorants 1-4 and includes positional isomers of Colorants 1-4;
Colorant B Composition is predominantly a mixture of Colorants 5-13 and includes positional isomers of Colorants 5-13;
Colorant C Composition is predominantly a mixture of Colorants 14-17 and includes positional isomers of Colorants 14-17.
The colorants described above may be employed in any amount effective for the intended purpose. In general, good results have been obtained when the colorant is present in an amount of from about 0.2 to about 10 wt. %, the humectant is present in an amount of from about 5 to about 70 wt. %, and the balance is water. A dye may also be added to the ink jet ink composition if desired.
The support for the ink jet recording element used in the invention can be any of those usually used for ink jet receivers, such as paper, resin-coated paper, plastics such as a polyester-type resin such as poly(ethylene terephthalate), polycarbonate resins, polysulfone resins, methacrylic resins, cellophane, acetate plastics, cellulose diacetate, cellulose triacetate, vinyl chloride resins, poly(ethylene naphthalate), polyester diacetate, various glass materials, and microporous materials such as microvoided polyester described in copending U.S. Ser. No. 09/656,129, filed Aug. 29, 2000, polyethylene polymer-containing material sold by PPG Industries, Inc., Pittsburgh, Pa. under the trade name of Teslin(copyright), Tyvek(copyright) synthetic paper (DuPont Corp.), and OPPalyte(copyright) films (Mobil Chemical Co.) and other composite films listed in U.S. Pat. No. 5,244,861. The thickness of the support employed in the invention can be, for example, from about 12 to about 500 xcexcm, preferably from about 75 to about 300 xcexcm.
Antioxidants, antistatic agents, plasticizers and other known additives may be incorporated into the support, if desired. In a preferred embodiment, paper is employed.
In a preferred embodiment of the invention, the ink-receiving layer is porous and contains inorganic particles such as silica, alumina, titanium dioxide, clay, calcium carbonate, barium sulfate, or zinc oxide. In another preferred embodiment, the porous ink-receiving layer comprises from about 30 wt. % to about 95 wt. % inorganic particles and from about 5 wt. % to about 70 wt. % polymeric binder, such as gelatin, poly(vinyl alcohol), poly(vinyl pyrrolidinone) or poly(vinyl acetate). The porous ink-receiving layer can also contain organic beads or polymeric micro-porous structures without inorganic filler particles as shown in U.S. Pat. Nos. 5,374,475 and 4,954,395, the disclosures of which are hereby incorporated by reference.
Examples of binders which may be used in the image-receiving layer include polyvinyl alcohol, polyvinyl pyrrolidone, poly(ethyl oxazoline), non-deionized or deionized Type IV bone gelatin, acid processed ossein gelatin or pig skin gelatin. The hydrophilic polymer may be present in an amount of from about 0.4 to about 30 g/m2, preferably from about 1 to about 16 g/m2.
The pH of the aqueous ink compositions employed in the invention may be adjusted by the addition of organic or inorganic acids or bases. Useful inks may have a preferred pH of from about 2 to 9, depending upon the type of dye being used. Typical inorganic acids include hydrochloric, phosphoric and sulfuric acids. Typical organic acids include methanesulfonic, acetic and lactic acids. Typical inorganic bases include alkali metal hydroxides and carbonates. Typical organic bases include ammonia, triethanolamine and tetramethylethylenediamine.
One or more humectants are employed in the ink jet composition employed in the invention to help prevent the ink from drying out or crusting in the orifices of the printhead. Examples of humectants which can be used include polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol 1,2,6-hexanetriol and thioglycol; lower alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol mono-methyl or mono-ethyl ether, propylene glycol mono-methyl or mono-ethyl ether, triethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol di-methyl or di-ethyl ether, and diethylene glycol monobutylether; nitrogen-containing cyclic compounds, such as pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone. Preferred humectants for the composition employed in the invention are diethylene glycol, glycerol, and diethylene glycol monobutylether.
Water-miscible organic solvents may also be added to the aqueous ink employed in the invention to help the ink penetrate the receiving substrate, especially when the substrate is a highly sized paper. Examples of such solvents include alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; ethers, such as tetrahydrofuran and dioxane; and esters, such as, ethyl lactate, ethylene carbonate and propylene carbonate.
Surfactants may be added to adjust the surface tension of the ink to an appropriate level. The surfactants may be anionic, cationic, amphoteric or nonionic. A preferred surfactant for the ink composition of the present invention is Surfynol(copyright) 465 (Air Products) at a final concentration of 0. 1% to 1.0%.
A biocide may be added to the composition employed in the invention to suppress the growth of micro-organisms such as molds, fungi, etc. in aqueous inks. A preferred biocide for the ink composition of the present invention is Proxel(copyright) GXL (Zeneca Specialties Co.) at a final concentration of 0.05-0.5 wt. %.
A typical ink composition employed in the invention may comprise, for example, the following substituents by weight: colorant (0.2-5%), water (20-95%), humectant (5-70%), water miscible co-solvents (2-20%), surfactant (0.1-10%), biocide (6.05-5%) and pH control agents (0.1-10%).
Additional additives that may optionally be present in the ink jet ink composition employed in the invention include thickeners, conductivity enhancing agents, anti-kogation agents, drying agents, and defoamers.
The image-recording layer used in the process of the invention employing the composition described above can also contain various known additives, including matting agents such as titanium dioxide, zinc oxide, silica and polymeric beads such as crosslinked poly(methyl methacrylate) or polystyrene beads for the purposes of contributing to the non-blocking characteristics and to control the smudge resistance thereof; surfactants such as non-ionic, hydrocarbon or fluorocarbon surfactants or cationic surfactants, such as quaternary ammonium salts; fluorescent dyes; pH controllers; anti-foaming agents; lubricants; preservatives; viscosity modifiers; dye-fixing agents; waterproofing agents; dispersing agents; UV-absorbing agents; mildew-proofing agents; mordants; antistatic agents, anti-oxidants, optical brighteners, and the like. A hardener may also be added to the ink-receiving layer if desired.
In order to improve the adhesion of the image-recording layer to the support, the surface of the support may be subjected to a treatment such as a corona-discharge-treatment prior to applying the image-recording layer.
In addition, a subbing layer, such as a layer formed from a halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl acetate copolymer can be applied to the surface of the support to increase adhesion of the image recording layer. If a subbing layer is used, it should have a thickness (i.e., a dry coat thickness) of less than about 2 xcexcm.
The image-recording layer may be present in any amount that is effective for the intended purpose. In general, good results are obtained when it is present in an amount of from about 2 to about 46 g/m2, preferably from about 6 to about 16 g/m2, which corresponds to a dry thickness of about 2 to about 42 xcexcm, preferably about 6 to about 15 xcexcm.